task: #1251

Author: Ivanbyone

README.md

@@ -55,6 +55,7 @@ Have a good contributing!
     - [1141. User Activity for the Past 30 Days I](./leetcode/easy/1141.%20User%20Activity%20for%20the%20Past%2030%20Days%20I.sql)
     - [1148. Article Views I](./leetcode/easy/1148.%20Article%20Views%20I.sql)
     - [1211. Queries Quality and Percentage](./leetcode/easy/1211.%20Queries%20Quality%20and%20Percentage.sql)
+    - [1251. Average Selling Price](./leetcode/easy/1251.%20Average%20Selling%20Price.sql)
     - [1327. List the Products Ordered in a Period](./leetcode/easy/1327.%20List%20the%20Products%20Ordered%20in%20a%20Period.sql)
     - [1378. Replace Employee ID With The Unique Identifier](./leetcode/easy/1378.%20Replace%20Employee%20ID%20With%20The%20Unique%20Identifier.sql)
     - [1407. Top Travellers](./leetcode/easy/1407.%20Top%20Travellers.sql)

leetcode/easy/1251. Average Selling Price.sql

@@ -0,0 +1,47 @@
+/*
+Question 1251. Average Selling Price
+Link: https://leetcode.com/problems/average-selling-price/description/?envType=study-plan-v2&envId=top-sql-50
+
+Table: Prices
+
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| product_id    | int     |
+| start_date    | date    |
+| end_date      | date    |
+| price         | int     |
++---------------+---------+
+(product_id, start_date, end_date) is the primary key (combination of columns with unique values) for this table.
+Each row of this table indicates the price of the product_id in the period from start_date to end_date.
+For each product_id there will be no two overlapping periods. That means there will be no two intersecting periods for the same product_id.
+ 
+
+Table: UnitsSold
+
++---------------+---------+
+| Column Name   | Type    |
++---------------+---------+
+| product_id    | int     |
+| purchase_date | date    |
+| units         | int     |
++---------------+---------+
+This table may contain duplicate rows.
+Each row of this table indicates the date, units, and product_id of each product sold. 
+ 
+
+Write a solution to find the average selling price for each product. average_price should be rounded to 2 decimal places. If a product does not have any sold units, its average selling price is assumed to be 0.
+
+Return the result table in any order.
+*/
+
+SELECT 
+    p.product_id,
+    COALESCE(ROUND(SUM(p.price * u.units) * 1.00 / SUM(u.units), 2), 0.00) AS average_price
+FROM Prices AS p
+LEFT JOIN
+    UnitsSold AS u
+    ON
+        p.product_id = u.product_id
+        AND u.purchase_date BETWEEN p.start_date AND p.end_date
+GROUP BY p.product_id